1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrostatic copying machine, a laser printer and the like. More particularly, the present invention relates to a medium conveying mechanism and a medium conveying method for conveying an output medium.
2. Description of the Related Art
In an electrophotographic copying machine or a printer, a predetermined surface potential is applied to a photosensitive member for holding an electrostatic latent image. The surface potential of the photo-sensitive member corresponding to a background portion or an image portion is selectively changed. Then, a developer image (toner image) obtained by supplying a developer (toner) to its portion is transferred to a material to be transferred (output medium).
The toner image transferred to the output medium is melted by a fixing unit. The toner image is then pressurized, and fixed to the output medium.
Incidentally, as the output medium, various types of media are utilized based on diversification of user's needs. The media are represented by sheets in a wide range of thicknesses from 50 to 250 g/m2, a transparent resin sheet, sealing paper and the like coated with a pressure sensitive adhesive.
Thus, in Japanese Patent Application Laid-Open Publication No. 2002-214964, there has been already proposed an example. In the example, an optimum value of conveying conditions or image forming conditions obtained by outputting a test pattern is stored in advance. The image forming conditions or the conveying conditions are set according to the stored optimum value when image formation based on the corresponding specific conveying conditions or image forming conditions are designated.
However, in the image forming apparatus disclosed in the above-mentioned document, it is disclosed that the degree of gloss of the fixed image is set to a constant level. In this case, the gloss is changed according to the fixing conditions. However, the change of the output image caused by the thickness of the output medium and the number of times by which the image formation was repeated (change with time/ages and wear of the conveying mechanism) and the like is not disclosed.
The type (thickness/material) of the output medium is in a wide range as described above. Accordingly, it is difficult to obtain equivalent reliability and durability for all the output media over a long period of time.